In a device such as a wireless headphone and a head-mounted display (for example, see Japanese Patent Application Laid-Open No. 2004-80679 (Patent Document 1)) which is mounted on the head to supply the video image and the sound, electric power is required for the output. A secondary battery such as a lithium-ion battery is frequently used as the electric power of the device. Because a large amount of energy is accumulated in the secondary battery such as the lithium-ion battery, sometimes firing or explosion is generated when usage of the secondary battery is mistaken. In order to prevent generation of such problems, usually a protective circuit or a protective mechanism is provided, and a cautionary statement is added to instructions so as to avoid use of an unregulated battery or an unregulated charging device.
However, there is a risk of generating the problems when a user disregards the cautionary statement and uses an inferior fake battery. Means for not charging the secondary battery while the device such as the wireless headphone and the head-mounted display is mounted on the head is required because the problems such as the firing and the explosion is frequently generated during charging. Therefore, for example, Japanese Utility Model Application Publication No. 7-22955 (Patent Document 2) discloses a structure in which the device cannot be mounted on the head during the charging by providing a charging terminal in a head band unit of the headphone.
Patent Document 1: Japanese Patent application Laid-Open No. 2004-80679
Patent Document 2: Japanese Utility Model application Publication No. 7-22955